Nutrient Pathways in Food Web of Tuggerah Lakes

This conceptual diagram shows a summary of the main nutrient pathways in Tuggerah Lakes, with the size of the yellow arrows scaled to represent the relative magnitude of each pathway. Dashed blue lines represent pathways not included in the modelling study but are inferred from the study on the diets of fish and invertebrates.

Ammonium (NH4+), nitrates (NO3-) and phosphates (PO43-) are common chemicals found in fertilisers and detergents. We call these ‘bio-available’ nutrients because they are readily taken up by microalgae (microscopic plants) and used for growth and metabolism. Phytoplankton are microalgae that live in the water column and benthic microalgae live on the sediment surface. Phytoplankton are constantly being eaten by zooplankton (microscopic animals) resulting in the tight control of the number of phytoplankton in the lake water. Wind and waves stir material up from the bottom and “resuspend” benthic microalgae which contribute to the standing stocks of phytoplankton in the lake.

Faecal pellets from the animals living in the lake, and dead animal/plant matter, deposit on the sea floor. Decaying organisms and faecal matter (“detritus”) are a major source of particulate organic nutrients in the sediments. Particulate organic nutrients are broken down by sediment bacteria releasing bio-available nutrients to the sediment and the lake. These bio-available nutrients are then taken up by all types of plants in the lake, by diffusion across their surface (phytoplankton, benthic microalgae, macroalgae, seagrass) or via roots/rhizomes in the sediment (seagrass).

Increasing the amount of bio-available nutrients in the lakes from catchment sources increases the amount of microalgae and macroalgae in the lakes because algae can take up these nutrients more readily than seagrass can.

Pelagic fish live in the water column and epibenthic fish live near the bottom of the lake. Fish can be herbivorous, carnivorous, detritivorous (eat detritus) and/or planktivorous (eat plankton). Find out more about what the fish and invertebrates are eating.